Earth's Crust in Motion

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Vocabulary

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Earthquake : A shaking that results in the movement of Earth's surface.
Shearing : Stress that pushes a mass of rock in opposite directions.
Tension :Stress that stretches rock so that it becomes thinner in the middle.
Compression :Stress that squeezes rock together until it folds or breaks.
Deformation :A change in the volume or shape of Earth's crust.
Fault : A break in Earth's crust where slabs of rock slip past each other.
Strike-slip fault : A fault where rocks on either side move past each other sideways with little up or down motion.
Normal fault : A type of fault where the hanging wall slides down; caused by tension in the crust.
Hanging wall : The slab of rock that forms the upper half of a fault.
Footwall : The slab of rock that forms the lower half of a fault.
Reverse fault : A fault where the hanging wall slides upward.
Fault-block mountain : A mountain that forms where a normal fault uplifts a slab of rock.
Anticline : An upward fold in rock formed by compression of Earth's crust.
Syncline : A downward fold in rock formed by compression in Earth's crust.
Plateau :A landform that has more or less level surface and is elevated high above sea level.
Folds : A bend in rock that forms where part of Earth's crust is compressed.

Outline

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Stress in the crust

• The movement of Earth's plates are powerful forces that changes the rocks in the crust.
  • These forces are examples of stress.
    • Stress is a force, so it adds energy to the rock.
      • Energy is stored in the rock until it either breaks or changes shape.

Types of Stress

• There are three kinds of stress: Shearing, tension, and compression
  • Shearing
    • Shearing can cause rock to become very brittle, and eventually snap.
  • Tension
    • Tension pulls on the crust, so it gets much thinner in the middle of the crust/rock.
      • Tension occurs when two plates are moving apart.
  • Compression
    • Compression squeezes rock until it folds or breaks.
  • Any change in the volume or the shape of the Earth's crust is called:Deformation..
    • Most changes occur very slowly.
      • They cannot be observed directly.
      • The slow shift of Earth's plates causes deformation.

Kinds of faults

• There are three types of faults: Strike-Slip faults, Normal faults, and reverse faults
  • Strike-Slip Fault
    • Shearing creates strike-slip faults.
    • An example of a strike slip fault is a transform boundary.
  • Normal Fault
    • Tension forces causes normal faults.
      • The fault is at an angle, so one piece of rock lies above the other.
      • The half of the fault that lies above is called the hanging wall.
      • The half of the fault that lies below is called the footwall.
  • Reverse Fault
    • A reverse fault has the same structure as a normal fault, but the blocks move in opposite directions.
    • The hanging wall lies below
    • The footwall lies above.

Friction Along Faults

• Friction is the force that opposes the motion of one surface as it moves across another surface.
  • Friction exists because surfaces are not perfectly smooth

Mountain Building

• Mountains Formed by Faulting
  • When a normal fault uplifts a block of rock, a fault-block mountain forms.
    • The Sierra Nevada of California is a fault-block mountain.
• Mountains formed by folding
  • Under certain conditions, plate movement causes the crust to fold and bend.
  • Folds are bends in rock that form when compression shortens and thickens part of earth's crust.

• Anticlines and Synclines
  • Geologists use the terms anticlines and synclines to describe upward and downward folds in rock.
  • A fold in rock that bends upwards into an arch is called an anticline.
  • A fold in rock that bends downwards into an arch is called an syncline.
• Plateaus
  • A plateau is a large area if flat land elevated high above sea level.
    • Sometimes plateaus form when vertical faults push up a large,flat block of rock.

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